This invention relates to a hermetically sealed flat-type piezo-electric oscillator assembly, and more specifically relates to the piezo-electric oscillator assembly, a flat-type package for the assembly, a lid for sealing the package, a metal frame of the package, a set of the piezo-electric oscillator assemblies, a set of the packages, and a set of the lids.
A piezo-electric oscillator will produce an electric signal in the form of oscillation which is in direct proportion to the amount of electric, acoustical or mechanical energy applied to the oscillator. Examples of the piezo-electric oscillators include quartz crystal oscillator and ceramic resonaters.
Quartz crystal is very stable in the physical and chemical properties, and shows little oscillatory loss. Because of these advantageous characteristics, the quartz crystal is particularly considered to be suitable to give an excellent piezo-electric oscillator element. Accordingly, quartz crystal oscillator elements are practically employed in a wide variety of arts. Moreover, the quartz crystal oscillator element is recently under advantageous conditions in the practical uses, that is, large-sized quartz crystals of good quality are now prepared with no difficulty and are subjected to the practical uses in place of natural quartz crystals; and a great number of quartz crystal oscillator elements of high quality are now supplied stably and at economical prices under the influence of improvements in the process for the manufacture of oscillator elements. For these reasons, the quartz crystal oscillator element now finds a wide variety of uses, such as, oscillation source in electronic circuits of watch, telecommunication device, etc.
For the use of the quartz crystal oscillator element as the oscillation source for the electronic circuits, it is required that the temperature coefficient of the resonance frequency is at a sufficiently low level; that the secular change is substantially none; and that "Q", namely the quality factor, is at a satisfactory high level. Moreover, it is required for facilitating the handling of the oscillation source that the oscillator element be stable against mechanical vibrations given from the outside and has a simple structure.
For satisfying these requirements, the quartz crystal oscillator element is generally employed in an assembly form encasing the element; that is, the element is encased in an appropriate hermetically sealed container to keep the element from influence of undesired outer conditions such as changes of humidity and atmospheric pressure and entry of contaminants. For instance, the high-stability oscillator element having the ratio of frequency change at a level of 10.sup.-8 -10.sup.-9 /year is encased in a hermetically sealed container in which the internal condition is kept under sufficiently high vacuum such as at a pressure of lower than 10.sup.-4 mm Hg, so as to ensure the oscillator element against variation of humidity and pressure in the outside of the container. The stabilization of frequency is furthermore ensured against change of conditions of the oscillator circuit by upgrading the Q value.
More recently, the quartz crystal oscillator assembly, namely, an encased oscillator, is employed extensively as the oscillation source for wristwatches. For this use, the oscillator assembly necessarily is prepared in a very small size, still maintaining the stability of oscillation characteristics as described above.
As described before, a large sized quartz crystal of good quality is now artificially prepared, and a thin plate having the crystal axis direction in alignment is easily obtained by slicing the large sized artificial quartz crystal. The so obtained thin plate of the quartz crystal is processed by a method conventionally employed in the art of semiconductor technology, such as the photoetching, to give an extremely small sized tuning-fork oscillator element of the "U" shape. A tuning-fork quartz crystal oscillator element employed in an electronic wristwatch, for instance, is in a U shape of the width of approximately 0.6 mm, the length of approximately 3.5 mm, and the thickness of 0.05-0.15 mm. This extremely small sized oscillator element is, as described before, kept under vacuum in a hermetically sealed container to form an oscillator assembly so that the oscillator element can function as desired.
In a practical view, the oscillator element is generally connected to lead wire to supply the element with electric energy such as voltage to induce an oscillation, and further another lead wire is generally provided under insulation to the oscillator element to recover the oscillation signal. One lead wire can serve as either for supplying the electric energy or for recovering the oscillation signal.
Accordingly, a piezo-electric oscillator such as the quartz crystal oscillation is generally in the form of an oscillator assembly comprising a piezo-electric oscillator element, a hermetically sealable container, and a plurality of lead wires passing under insulation through the container from the outside to the inside of the container.
A representative quartz crystal oscillator assembly which is now employed as the oscillation source of an electronic wristwatch, is one whose container is in a small sized cylindrical shape. The oscillator assembly of this type comprises a hollow cylinder, whose one end is closed at the top and another end is open at the bottom; an insulating material portion provided to the open bottom of the cylinder in such a manner that the cylinder is hermetically sealed; a couple of lead wires passing through the insulating material portion from the outside to inside of the cylinder so as to provide a couple of terminals inside of the cylinder; and a quartz crystal oscillator element encased in the cylinder and mounted on the terminals by one end.
The cylindrical-shape quartz crystal oscillator assembly is employed in a great number as the oscillation source of an electronic wristwatch of a conventional type.
More recently, since a need for an electronic wristwatch of a smaller thickness than the conventional one increases, the parts and devices to be included in the wristwatch are under requirement to reduce their volumes. This requirement is naturally directed to the oscillator assembly, as well as to other parts of the wristwatch. Furthermore, a variety of electronic devices utilizing the quartz crystal oscillator assembly is likewise under requirements to reduce their volumes. Therefore, the reduction of the volume of a piezo-electric oscillator assembly such as the quartz crystal oscillator assembly is one of the principal subjects under study in the art.
The conventional cylindrical-shape piezo-electric oscillator assembly is not high in the volume efficiency, as understood from comparison between the thin-plate shaped oscillator element and the cylindrical-shape container. One of the countermeasures for avoiding the power volume efficiency is variation of the section of the cylinder from the round to an oval. However, the hollow cylindrical container with the oval section is not easy in the manufacture, because the procedures involved in the manufacture of the cylindrical container with the oval section are more complicated than the procedures involved in the manufacture of the conventional cylindrical container. Moreover, the yield of acceptable final products against the total number of the final products is apt to become poor due to the complicated procedures involved. Accordingly, this modification is not considered to be practically applicable.
From another view-point, the cylindrical container has a disadvantageous feature in addition to the problem of the poor volume efficiency. At present, the electronic circuits for an electronic wristwatch is apt to be arranged in the system of extremely small sized hybrid module, for complying with the up-to-date requirements for a further smaller sized and thinner electronic wristwatch. The cylindrical-shape oscillator assembly is not advantageously applied to the hybrid module system, because the cylinder can not be suitably mounted on a base plate of the module system.
In view of these requirements, it can be thought that the container of the oscillator assembly be so changed as to have flat shape, that is, flat box-like shape.
As a flat-type container for an element conventionally employed in the electronics technology art, there can be mentioned a flat-type container for hermetically sealing a semiconductor element to give a semiconductor assembly. The flat-type container for a semiconductor element generally consists of a couple of metal frames, one serving as a lid, namely, a covering plate, and another serving as a bottom plate; and insulating material portion such as a glass material portion provided between the two plates to serve as the side wall to seal hermetically the container; and a plurality of lead wires passing through the side wall of the insulating material from the outside to the inside of the container. A container of this type is generally employed for the manufacture of a semiconductor assembly, whose dimensions are in centimeter order.
A trial for converting the above-described flat-type container employed for semiconductor to apply to the container for the small sized piezo-electric oscillator assembly fails to give satisfactory result. This is because the reduction of dimension of the container produces poor sealability due to the accompanying reduction of the sealing area.
As is known, there is a certain degree of difference of the thermal expansion coefficient between a metal and an insulating material such as glass. Even in a very matching combination of a metal and an insulating material, there inherently is a little difference of the thermal expansion coefficient between them. Accordingly, the heating process for joining the insulating material portion to the metal frames necessarily imposes a certain amount of strain on the joining face. If the joining area is sufficiently large, the joining face is able to resist against the deforming force of the strain which is likely to break down the joining face. However, if the joining area is small, the joining face is not able to resist the deforming force, so that whole or a part of the joining face is broken down to result in leakage of the container. This is the case in the application of the flat-type container for semiconductor to the flat-type container for the piezo-electric oscillator. The leakage of the container is, naturally, fatal to the oscillator assembly employed in practice. Therefore, the simple application of the flat-type container generally employed for semiconductor is not able to solve the aforementioned problems caused by the use of the conventional cylindrical container for piezo-electric oscillator.
It is, therefore, one object of this invention to provide a hermetically sealed flat-type piezo-electric oscillator assembly that is able to be constituted in an extremely small size.
It is another object of this invention to provide a hermetically sealed flat-type piezo-electric oscillator assembly showing an excellent oscillation characteristics.
It is further object of this invention to provide a hermetically sealed flat-type piezo-electric oscillator assembly that can be suitably mounted on a base plate of the module system.
It is still further object of this invention to provide a hermetically sealed flat-type piezo-electric oscillator assembly whose oscillation characteristics are easily adjustable after completion of production of the oscillator assembly.
It is still further object of this invention to provide a flat-type package for a hermetically sealed flat-type piezo-electric oscillator assembly.
It is still further object of this invention to provide a lid for hermetically sealing a flat-type package for a piezo-electric oscillator assembly.
It is still further object of this invention to provide a set of the hermetically sealed flat-type piezo-electric oscillator assemblies which is suitably handled in a mass production system.
It is still further object of this invention to provide a set of the flat-type packages and a set of the lids which are suitable to produce the hermetically sealed flat-type piezo-electric oscillator assemblies in a mass production system.
Other objects and advantages of this invention will become apparent upon reading the detailed discription given herein and with reference to the accompanying drawings.